Structure and method for forming interconnect structure

ABSTRACT

A method for forming a semiconductor structure includes providing a semiconductor substrate and forming a dielectric layer over the semiconductor substrate. An opening is formed in the dielectric layer. A conductive line is formed in the opening, wherein the conductive line has an open void formed therein. A sealing metal layer is formed overlying the conductive line, the dielectric layer, and the open void, wherein the sealing metal layer substantially fills the open void. The sealing metal layer is planarized so that a top surface thereof is substantially level with a top surface of the conductive line. An interconnect feature is formed above the semiconductor substrate, wherein the interconnect feature is electrically coupled with the conductive line and the sealing metal layer-filled open void.

BACKGROUND

In semiconductor technology, an integrated circuit pattern can be formed on a substrate using various processes including a photolithography process, ion implantation, deposition and etch. Damascene processes are utilized to form multilayer copper interconnections including vertical interconnection vias and horizontal interconnection metal lines. During a damascene process, trenches are formed in a dielectric material layer, metal such as copper or tungsten is filled in the trenches, then a chemical mechanical polishing (CMP) process is applied to remove excess metal on the dielectric material layer and planarize the top surface.

As the integrated circuit (IC) fabrication moves to advanced technology nodes, the IC feature size scales down to smaller dimensions. For example, the trench dimensions get smaller and smaller and as a result filling the metal layer in the trench becomes increasingly difficult. Oftentimes, a void, seam, or pit is formed after the metal layer is deposited. The poor step coverage of the barrier/adhesion layer and the metal layer, the small feature size of the trench opening, and the high aspect ratio of the opening all can contribute to the formation of voids. Voids in the metal film can trap impurities inside and can be opened up during the planarization process after the metal film deposition. A buried void or a void that is opened can degrade device yield and cause reliability problems, such as delamination and electro-migration during reliability testing. Moreover, a subsequent interconnect feature, such as a metal line that lands on and makes electrical contact with the underlying metal film having a void therein can degrade device performance and cause reliability problems.

Accordingly, a structure and method for forming an interconnect structure are needed to address the above issues.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart of a method of fabricating a semiconductor device having an interconnect structure according to various embodiments of the present disclosure.

FIGS. 2-6 b are cross-sectional views of a portion of an interconnect structure on a semiconductor device at various stages of fabrication, according to one embodiment of the present disclosure.

FIGS. 2-4 and 7 a-7 b are cross-sectional views of a portion of an interconnect structure on a semiconductor device at various stages of fabrication, according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

In the following description, specific details are set forth to provide a thorough understanding of embodiments of the present disclosure. However, one having ordinary skill in the art will recognize that embodiments of the disclosure can be practiced without these specific details. In some instances, well-known structures and processes are not described in detail to avoid unnecessarily obscuring embodiments of the present disclosure.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are intended for illustration.

FIG. 1 is a flowchart of a method 2 for fabricating a semiconductor device having an interconnect structure according to various aspects of the present disclosure. Referring to FIG. 1, the method 2 includes block 4, in which a semiconductor substrate is provided. The method 2 includes block 6, in which a dielectric layer is formed on the semiconductor substrate. The method 2 includes block 8, in which an opening is formed in the dielectric layer. The method 2 includes block 10, in which a conductive line is formed in the opening. The conductive line has an open void formed therein. The method 2 includes block 12, in which a sealing metal layer is formed overlying the conductive line, the dielectric layer, and the open void. The sealing metal layer substantially fills the open void. The method 2 includes block 14, in which the sealing metal layer is planarized so that a top surface thereof is substantially level with a top surface of the conductive line. The method 2 includes block 16, in which an interconnect feature is formed above the semiconductor substrate. The interconnect feature is electrically coupled with the conductive line and the sealing metal layer-filled open void.

It is understood that additional processes may be performed before, during, or after the blocks 4-16 shown in FIG. 1 to complete the fabrication of the semiconductor device, but these additional processes are not discussed herein in detail for the sake of simplicity.

FIGS. 2-7 b are diagrammatic fragmentary cross-sectional side views of a semiconductor device at various fabrication stages according to embodiments of the method 2 of FIG. 1. It is understood that FIGS. 2-7 b have been simplified for a better understanding of the inventive concepts of the present disclosure. It should be appreciated that the materials, geometries, dimensions, structures, and process parameters described herein are exemplary only, and are not intended to be, and should not be construed to be, limiting to the invention claimed herein. Many alternatives and modifications will be apparent to those skilled in the art, once informed by the present disclosure.

FIGS. 2-6 b are cross-sectional views of an interconnect structure on a semiconductor device, according to one embodiment of the present disclosure.

Referring now to FIG. 2, a semiconductor device 100 is provided. The semiconductor structure 100 includes a substrate 110 and a first dielectric layer 120 having openings 130 therein. The substrate 110 may include silicon or other elementary semiconductors such as germanium. The substrate 110 may be a single crystalline or a compound semiconductor substrate. The substrate 110 can contain features and device regions. For example, underneath openings 130, there can be a contact or a metal structure that provides electrical connection to device regions in the substrate 110 (not shown).

Openings 130 may be trenches for forming metal lines. Alternatively, openings 130 can be vias (holes), contacts (holes) or other patterns into which a conductive layer is to be formed. In an exemplary embodiment, first dielectric layer 120 has a low dielectric constant (k value), preferably lower than about 3.0. More preferably, first dielectric layer 120 has a k value of less than about 2.5. First dielectric layer 120 may include commonly used materials such as carbon-containing dielectric materials, and may further contain nitrogen, hydrogen, oxygen, and combinations thereof. A porous structure is preferred for lowering the k value. The preferred thickness of first dielectric layer 120 is between about 1,000 Angstroms and about 3,500 Angstroms. One skilled in the art will realize, however, that the dimensions recited throughout the description are related to the technology used for forming the integrated circuits, and will reduce with the change of the formation technology.

Openings 130 may be formed by photolithography techniques known in the art. Generally, photolithography techniques involve applying a photoresist material (not shown) and exposing the photoresist material in accordance with a desired pattern. The photoresist material is then developed to remove a portion of the photoresist material, thereby exposing the underlying material in accordance with the desired pattern. The remaining photoresist material protects the underlying material from subsequent processing steps, such as etching, performed to form the openings 130 in the first dielectric layer 120. The etching process may be a wet or dry, anisotropic or isotropic, etch process. After the openings 130 are formed in the first dielectric layer 120, the remaining photoresist, if any, may be removed. Other processes, such as electron beam lithography (EBL) or the like, may be utilized to form openings 130.

It should be noted that the process discussed above described a single-damascene process for illustrative purposes only. Other processes, such as a dual-damascene process may be utilized in accordance with an embodiment of the present invention. For example, a dual-damascene process may be utilized to form a trench and a via through one or more layers of the first dielectric layer 120.

FIG. 3 illustrates the formation of first diffusion barrier layer 140 and conductive material layer 150 in openings 130. The first diffusion barrier layer 140 provides an effective prevention from metal diffusion into the first dielectric layer 120. First diffusion barrier layer 140 is blanket deposited over substrate 110 using physical vapor deposition (PVD) or one of the chemical vapor deposition (CVD) methods to line openings 130. First diffusion barrier layer 140 preferably includes titanium, titanium nitride, tantalum, tantalum nitride, cobalt, or other alternatives. The thickness of first diffusion barrier layer 140 may be between about 20 Angstroms and about 200 Angstroms.

After the first diffusion barrier layer 140 is deposited, conductive material layer 150 is deposited over substrate 110. Conductive material layer 150 may include copper, copper alloys, aluminum, aluminum alloys, tungsten, silver, gold, combinations of these, or other conductive materials. Some exemplary processes usable to deposit conductive material layer 150 may include chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), electroplating, electroless deposition, or other suitable methods.

A void 160 is often formed after the conductive material layer 150 is deposited. The poor step coverage of the first diffusion barrier layer 140 and the conductive material layer 150, the small feature size of openings 130, and the high aspect ratio of openings 130 all can contribute to the formation of void 160. Void 160 can form anywhere in opening 130. For example, void 160 can form at or near the center of opening 130, near a top or a bottom of opening 130, or near a sidewall of first diffusion barrier layer 140.

As shown in FIG. 4, a chemical mechanical polish (CMP) is then performed to remove excess conductive material on first dielectric layer 120, so that a top surface of conductive material layer 150 is substantially level with a top surface of first dielectric layer 120 leaving first diffusion barrier layer 140 and first conductive lines 170 only in openings 130. The planarization step also opens up void 160.

An optional pretreatment may be performed to treat the surface of first conductive lines 170. The pretreatment has the function of removing impurities along the surface of the first conductive lines 170 and/or reducing native copper oxide to copper.

Referring now to FIG. 5, a sealing metal layer 175 is deposited over the first conductive lines 170, portions of the first diffusion barrier layer 140, the first dielectric layer 120, and the open voids 160. The sealing metal layer 175 is a conductive material that substantially fills and seals the open voids 160. By eliminating buried voids or voids that are opened in first conductive lines 170, the sealing metal layer 175 provides a reliable interconnection between first conductive lines 170 and an interconnect feature, such as a metal line that lands on and makes electrical contact with first conductive line 170.

The sealing metal layer 175 is formed by one of chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced chemical vapor deposition (PECVD), metal-organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), plasma-enhanced atomic layer deposition (PEALD), or any other suitable deposition processes. A material of the sealing metal layer 175 may include cobalt (Co), copper (Cu), tungsten (W), aluminum (Al), manganese (Mn), ruthenium (Ru), and their combinations. In another embodiment, a material of the sealing metal layer 175 includes oxides, nitrides, and their combinations.

As shown in FIG. 6 a, a chemical mechanical polish step is then performed to remove excess sealing metal layer 175 so that a top surface of the sealing metal layer 175 is substantially level with a top surface of the first conductive line 170.

An interconnect feature 199 having second conductive lines 200 embedded in a second dielectric layer 180 is formed over substrate 110, as shown in FIG. 6 b. The interconnect feature 199 may be a metal line, a contact, or a metal via. Second conductive lines 200 are aligned with and land on a respective one of the first conductive lines 170 and the sealing metal layer 175 or, in other words the sealing metal layer-filled open void. Particularly, one of the second conductive lines 200 contacts a respective one of the first conductive lines 170 and the sealing metal layer-filled conductive line 170, providing an electrical path. In one embodiment, second conductive lines 200 are formed by patterning the second dielectric layer 180 to form a trench, filling various conductive materials in the trench, and performing a chemical mechanical polishing (CMP) process to remove various conductive materials on the second dielectric layer 180. In one example, patterning the second dielectric layer 180 includes a lithography process and an etching process. The lithography process forms a patterned photoresist layer having an opening that defines a region for the trench. The etching process may include two etch steps to respectively remove the second dielectric layer 180 and an optional etch stop layer 177 within the opening of the patterned photoresist layer. The patterned photoresist layer is removed by wet stripping or plasma ashing after the etching. Alternatively, a hard mask may be used as an etch mask in the process to form the trench.

In some embodiments, a second diffusion barrier layer 190 may be formed between the second dielectric layer 180 and a respective one of the second conductive lines 200. In some embodiments, an etch stop layer 177 may be formed between the interconnect feature 199 and the first dielectric layer 120 and the first sealing metal layer-filled conductive lines 170. The etch stop layer 177 protects the underlying structures, such as first dielectric layer 120, and also provides improved adhesion for subsequently formed layers. The etch stop layer 177 preferably has a dielectric constant of less than about 4.0, and may comprise materials such as SiC, SiCN, SiCO, SiN, carbon-based materials, and combinations thereof. The preferred thickness of the etch stop layer 177 is between about 200 Angstroms and about 1,000 Angstroms.

FIGS. 2-4 and 7 a-7 b are cross-sectional views of an interconnect structure on a semiconductor device 100, according to another embodiment of the present disclosure. The process steps for forming the semiconductor device 100 described above with reference to FIGS. 2-4 are the same in this embodiment and therefore will not be repeated again. FIG. 7 a illustrates metal caps or sealing metal caps 177 formed on first conductive lines 170. The sealing metal caps 177 preferably comprise materials such as cobalt, nickel, tungsten, molybdenum, silicon, zinc, chrome, boron, phosphorus, nitrogen, and combinations thereof. Sealing metal caps 177 may also be composite layers comprising more than one layer, wherein each of the layers includes one or more of the above-discussed materials. The thickness of the sealing metal caps 177 in an exemplary embodiment is between about 5 Angstroms and about 1,000 Angstroms, and more preferably between about 10 Angstroms and about 100 Angstroms.

In an exemplary embodiment, sealing metal caps 177 are formed by electroless plating and are selectively formed only on exposed surfaces of first conductive lines 170, the sealing metal caps 177 filling the voids 160 in the first conductive lines 170. One advantageous feature of selective formation of sealing metal caps 177 is that top surfaces of sealing metal caps 177 may be deposited higher, level with, or lower, than the respective diffusion barrier layers 140, depending on the design requirements. Electroless plating is preferably performed, for example, by using a plating liquid containing cobalt ions, a complexing agent, a pH buffer, a pH adjusting agent, and an alkylamine borane as a reducing agent. Depending on the preferred composition of sealing metal caps 177, the plating liquid may further contain refractory (high-melting point) metals such as tungsten ions or molybdenum ions. The cobalt ions contained in the plating liquid may be supplied from a cobalt salt, for example, cobalt sulfate, cobalt chloride or cobalt acetate. Other desired components preferred in sealing metal caps 177 are also included in the plating liquid in the form of ions. The structure formed in the previously discussed steps is submerged in the plating liquid, wherein the temperature of the plating liquid is in a range of between about 30 Celsius and about 90 Celsius according to one embodiment.

In the exemplary embodiment shown in FIG. 7 a, the sealing metal caps 177 are selectively formed only on the first conductive lines 170 and the first diffusion barrier layers 140, but not on top edges of the first dielectric layer 120. This may be achieved by using a non-palladium catalyst, thus enabling a direct electroless plating. In other embodiments, sealing metal caps 177 can be formed by depositing a metal cap layer using common techniques such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), metal-organic chemical vapor deposition (MOCVD), and atomic layer deposition (ALD), and then etching the metal cap layer to form sealing metal caps 177.

Referring now to FIG. 7 b, an interconnect feature 201 having second conductive lines 200 embedded in a second dielectric layer 180 is formed over substrate 110. The interconnect feature 201 may be a metal line, a contact, or a metal via. Second conductive lines 200 are aligned with and land on the sealing metal caps 177 to provide an electrical path. In one embodiment, the second conductive lines 200 are formed by patterning the second dielectric layer 180 to form a trench, filling various conductive materials in the trench, and performing a chemical mechanical polishing (CMP) process to remove various conductive materials on the second dielectric layer 180. In one example, patterning the second dielectric layer 180 includes a lithography process and an etching process. The lithography process forms a patterned photoresist layer having an opening that defines a region for the trench. The etching process may include two etch steps to respectively remove the second dielectric layer 180 within the opening of the patterned photoresist layer. The patterned photoresist layer is removed by wet stripping or plasma ashing after the etching. Alternatively, a hard mask may be used as an etch mask in the process to form the trench.

In some embodiments, a second diffusion barrier layer 190 may be formed between the second dielectric layer 180 and a respective one of the second conductive lines 200. In some embodiments, an etch stop layer 178 may be formed between the interconnect feature 201 and the first dielectric layer 120, the sealing metal caps 177, and the first conductive lines 170. The etch stop layer 178 protects the underlying structures, such as first dielectric layer 120, and also provides improved adhesion for subsequently formed layers. The etch stop layer 178 preferably has a dielectric constant of less than about 4.0, and may comprise materials such as SiC, SiCN, SiCO, SiN, carbon-based materials, and combinations thereof. The preferred thickness of the etch stop layer 178 is between about 200 Angstroms and about 1,000 Angstroms.

In the preceding paragraphs, single damascene processes are discussed. One skilled in the art will realize that the teaching is readily available for dual damascene processes.

Advantages of one or more embodiments of the present disclosure provide for a more reliable and robust interconnect structure for advanced semiconductor manufacturing technologies. As voids, seams, or pits in a lower metal line are sealed, a foundation having good electrical and reliability performance is provided for a top metal line or via to land on the lower metal line.

The present disclosure has described various exemplary embodiments. According to one embodiment, a method for forming a semiconductor structure includes providing a semiconductor substrate and forming a dielectric layer over the semiconductor substrate. An opening is formed in the dielectric layer. A conductive line is formed in the opening, wherein the conductive line has an open void formed therein. A sealing metal layer is formed overlying the conductive line, the dielectric layer, and the open void, wherein the sealing metal layer substantially fills the open void. The sealing metal layer is planarized so that a top surface thereof is substantially level with a top surface of the conductive line. An interconnect feature is formed above the semiconductor substrate, wherein the interconnect feature is electrically coupled with the conductive line and the sealing metal layer-filled open void.

According to another embodiment, a method for forming a semiconductor structure includes providing a semiconductor substrate and forming a first dielectric layer over the semiconductor substrate. An opening is formed in the dielectric layer. A conductive line is formed in the opening, wherein the conductive line has an open void formed therein. A sealing metal cap is formed on the first conductive line, the sealing metal cap substantially filling the open void. A second conductive line is formed embedded in a second dielectric layer, the second conductive line electrically contacting the sealing metal cap.

According to yet another embodiment, a semiconductor structure includes a first dielectric layer on a semiconductor substrate, the first dielectric layer having a conductive line with an open void formed therein. The semiconductor structure also includes a sealing metal layer substantially in the open void having a top surface thereof substantially level with a top surface of the conductive line, and an interconnect feature embedded in a second dielectric layer and electrically contacting the conductive line and the sealing metal layer-filled open void.

In the preceding detailed description, specific exemplary embodiments have been described. It will, however, be apparent to a person of ordinary skill in the art that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the present disclosure. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that embodiments of the present disclosure are capable of using various other combinations and environments and are capable of changes or modifications within the scope of the claims. 

What is claimed is:
 1. A method for forming a semiconductor structure, comprising: providing a semiconductor substrate; forming a dielectric layer over the semiconductor substrate; forming an opening in the dielectric layer; forming a conductive line in the opening, wherein the conductive line has an open void formed therein; forming a sealing metal layer overlying the conductive line, the dielectric layer, and the open void, wherein the sealing metal layer substantially fills the open void; planarizing the sealing metal layer so that a top surface thereof is substantially level with a top surface of the conductive line; and forming an interconnect feature above the semiconductor substrate, wherein the interconnect feature is electrically coupled with the conductive line and the sealing metal layer-filled open void.
 2. The method of claim 1, further comprising: forming a diffusion barrier layer disposed on sidewalls of the opening.
 3. The method of claim 1, wherein the step of forming a conductive comprises: depositing a conductive material layer over the semiconductor substrate to line the opening, wherein a void is formed substantially at the center of, or slightly near a top, or slightly near a side of the opening; and planarizing the semiconductor substrate so a top surface of the conductive material layer is substantially level with a top surface of the dielectric layer, thus forming the open void.
 4. The method of claim 1, wherein the sealing metal layer is formed by one of chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced chemical vapor deposition (PECVD), metal-organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), or plasma-enhanced atomic layer deposition (PEALD).
 5. The method of claim 1, wherein the interconnect feature is a metal line.
 6. The method of claim 1, further comprising forming an etch stop layer on the dielectric layer, the conductive line, and the sealing metal-filled open void.
 7. A method for forming a semiconductor structure, comprising: providing a semiconductor substrate; forming a first dielectric layer over the semiconductor substrate; forming an opening in the first dielectric layer; forming a first conductive line in the opening, wherein the first conductive line has an open void formed therein; forming a sealing metal cap on the first conductive line, the sealing metal cap substantially filling the open void; and forming a second conductive line embedded in a second dielectric layer and electrically contacting the sealing metal cap.
 8. The method of claim 7, further comprising: forming a diffusion barrier layer disposed on sidewalls of the opening.
 9. The method of claim 7, wherein the step of forming the first conductive line comprises: depositing a conductive material layer over the semiconductor substrate to line the opening, wherein a void is formed substantially at the center of, or slightly near a top of, or slightly near a side of the opening; and planarizing the semiconductor substrate so that a top surface of the conductive material layer is substantially level with a top surface of the dielectric layer, thus forming the open void.
 10. The method of claim 7, wherein the sealing metal cap is formed by one of chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), metal-organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), or electroless plating.
 11. The method of claim 7, wherein the sealing metal cap above a top surface of the first conductive line has a thickness of less than 1,000 Angstroms.
 12. The method of claim 11, wherein the sealing metal cap has a thickness between about 10 Angstroms and about 100 Angstroms.
 13. The method of claim 7, further comprising forming an etch stop layer on the first dielectric layer, the first conductive line, and the sealing metal cap.
 14. A method for forming a semiconductor structure, comprising: depositing a first dielectric layer on a semiconductor substrate; patterning the first dielectric layer to have an opening therein; forming within the opening a conductive line having an void formed therein; substantially filling the void with a sealing metal layer; planarizing a top surface of the sealing metal layer to be substantially level with a top surface of the conductive line; depositing a second dielectric layer over the sealing metal layer and the conductive line; and forming in the second dielectric layer an interconnect feature electrically contacting the conductive line and the sealing metal layer.
 15. The method of claim 14, further comprising: planarizing the conductive line so that the top surface of the conductive line is substantially level with a top surface of the first dielectric layer.
 16. The method of claim 15, wherein the step of planarizing the conductive line causes formation of the void.
 17. The method of claim 14, further comprising: lining sidewalls of the opening with a diffusion barrier layer.
 18. The method of claim 14, wherein the step of substantially filling the void with a sealing metal layer includes depositing the sealing metal layer using a process selected from the group consisting of chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), metal-organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), electroless plating, and combinations thereof.
 19. The method of claim 14, wherein the sealing metal layer fills the void.
 20. The method of claim 14, wherein the sealing metal layer is selected from the group consisting essentially of cobalt, copper, tungsten, aluminum, manganese, ruthenium, oxides of the above, nitride of the above, and their combinations. 